FAA Aviation Mechanic Airframe (AMA)Airframe StructuresMedium
A composite technician applies a vacuum bag over a repair patch layup on a wing skin prior to curing. What is the primary purpose of the vacuum bag in this process?
- ATo apply uniform atmospheric pressure that compacts the plies and removes trapped air and excess resin
- BTo provide ultraviolet protection to the resin during cure
- CTo directly heat the resin to its cure temperature
- DTo mix the resin and hardener together evenly
Show answer & explanationAnswer & explanation
Correct answer: A. To apply uniform atmospheric pressure that compacts the plies and removes trapped air and excess resin
Vacuum bagging evacuates air from within a sealed bag placed over the layup, allowing atmospheric pressure (about 14.7 psi at sea level) to compact the plies uniformly, squeeze out trapped air and excess resin, and improve the fiber-to-resin ratio and bond quality.
Why the other options are wrong
- B. Vacuum bags do not provide UV protection; that is unrelated to their function.
- C. Heat for cure typically comes from a heat blanket, oven, or autoclave, not the vacuum bag itself.
- D. Resin and hardener are mixed before layup, not by the vacuum bag.
Vacuum Bagging
A composite curing technique where a sealed plastic bag is placed over the layup and air is evacuated, allowing atmospheric pressure to compact the plies and remove voids and excess resin during cure.
- Uses atmospheric pressure (~14.7 psi) for compaction
- Removes trapped air voids and excess resin
- Often combined with heat blankets or autoclave for cure
- Improves fiber-to-resin ratio and part strength
Memory trick: Vacuum squeezes the sandwich flat like a food-saver bag.